Astronomers redefine the habitable zone for exoplanets

The new definition of a star’s habitable zone will affect how we search for habitable exoplanets.Credit: PHL@UPR Arecibo / Rogelio Bernal Andreo

When searching for potentially habitable exoplanets, one of the key factors to take into consideration is the habitable zone, the region around a star where temperatures could allow liquid water to exist on the surface of any rocky planets that may orbit them.

In general, this region is neither too hot nor too cold, although other characteristics that could affect the surface temperature of a planet such as cloud cover must also be taken into consideration when estimating a planet’s possible habitability.

The “classic” habitable zone model has remained unchanged for some time, but now yesterday a group of astronomers have announced some modifications that will affect how many discovered exoplanets are considered to be in their stars’ habitable zones.

The astronomers, from Penn State and also collaborators with the Planetary Habitability Laboratory, have concluded that, overall, the habitable zones are a bit farther out from their stars than previously thought.

“This has implications for finding other planets with life on them,” according to Ravi Kumar Kopparapu, a lead investigator with the new study.

Just how does this affect the potentially habitable exoplanets already discovered? It means that some of them may not be in the newly-defined habitable zone after all, but also that some exoplanets previously considered to be outside the habitable zone will now be in it.

In our solar system, the “old” habitable zone extended from just inside the orbit of Venus to outside the orbit of Mars. Under the new definition, Earth would now reside very close to the inner edge of the habitable zone instead of Venus. Interesting, considering that Earth flourishes with life, even though it is now barely inside our Sun’s habitable zone.

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4 Comments

a1falang, it is habitable with most atmospheres. Earth primordial atmosphere was very differenet from the current one.

coacervate: It is based on updating the models with the latest GW parameters. As it happens, they make progress on how to define HZ (irradiance is a rough indicator) and how the inner edge behaves for M stars. But one must read the paper IMO.

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The Meridiani Journal is a chronicle of planetary exploration, both in our own solar system and beyond; the name is derived from the desert plains of Meridiani Planum on Mars, where the Opportunity rover landed in 2004, finding the first on-site evidence for past liquid water, including the famous geological "blueberries"... more